Production of homopolymers or copolymers of ethylene

ABSTRACT

Production of homopolymers or copolymers of ethylene by homopolymerization of ethylene or copolymerization of mixtures of ethylene and other monomers at superatmospheric pressure and elevated temperature under the influence of a free radical generating polymerization initiator with or without a polymerization regulator. The initiator used is a mixture of (a) an initiator having a halflife of ten to 30 hours at 50* C and (b) an initiator having a halflife of 0.2 to 10 hours at 50*C, the halflife at 50*C of initiator (a) being at least twice as long as that of initiator (b). Polymers having a high molecular weight and a low degree of branching are obtained in a fairly high yield.

United States Patent [191 Pfannmueller et a1.

1 Jan. 30, 1973 [541 PRODUCTION OF HOMOPOLYMERS OR COPOLYMERS OFETHYLENE [73] Assignee: Badische Anilin- & Soda-FabrikAktiengesellschait, Ludwigshafen am Rhine, Germany 22 Filed: Sept. 16,1970 211 App1.No.: 72,866

1,047,851 1 H1966 Great Britain ..260/94.9 R

OTHER PUBLICATIONS Kirk-Othmer, Encyclopedia of Chemical Technology,Vol. 14, pg. 81 1-813, lnterscience (1963) TP 9 E68 Encyclopedia ofPolymer Science and Technology Vol. 9, pg. 818-827, lnterscience TP156.P6E6

Primary ExaminerJames A. Seidleck Assistant Examiner-A. HollerAtt0rneylohnston, Root, OKeeffe, Keil, Thompson and Shurtleff [57]ABSTRACT Production of homopolymers or copolymers of [52] US. Cl...260/86.7, 260/63 R, 260/73 R, ethylene by homopolymerization ofethylene or 260/78.5 HC, 260/88.1,260/94 9 R copolymerization ofmixtures of ethylene and other [51] Int. Cl ..C08f 1/60, C08f 15/02mOnomerS at superatmospheric pressure and elevated [58] Field of Search..260/94.9 R, 86.7, 85.3 R,88.1 p under the influence of a free radicalR generating polymerization initiator with or without a polymerizationregulator. The initiator used is a mix- 5 References Cited ture of (a)an initiator having a halflife of ten to 30 hours at 50C and (b) aninitiator having a halflife of UNITED STATES PATENTS 0.2 to 10 hours at50C, the halflife at 50C of initiator 3,142,666 7/1964 Deex et al260/94.9 R (a) being at "i i as as that 9 inmaw' Polymers having a highmolecular weight and a low F REI N P EN OR APPLICATIONS degree ofbranching are obtained in a fairly high yield.

7 Claims, N0 Drawings 1,008,115 10/1965 Great Britain ..260/94.9R

PRODUCTION OF HOMOPOLYMERS OR COPOLYMERS OF ETHYLENE The presentinvention relates to a process for the production of homopolymers orcopolymers of ethylene by homopolymerization of ethylene or bycopolymerization of a mixture of 100 molar proportions of ethylene andup to 100 molar proportions of one or more other monomers which arecopolymerizable with ethylene, which have from three to twenty carbonatoms and which are ethylenically unsaturated, at a pressure of from 800to 7,000 atmospheres and at a temperature of from 150 to 260 C under theinfluence of a free radical generating polymerization initiator with orwithout a polymerization regulator.

In prior art methods of this type there is a general rule that (underotherwise identical conditions) relatively small yields are obtained atrelatively low temperatures and relatively large yields at relativelyhigh temperatures. There is also the rule that (under otherwiseidentical conditions) polymers having a relatively high molecular weightand a relatively low degree of branching are obtained at relatively lowtemperatures, while polymers having a relatively low molecular weightand a relatively high degree of branching are obtained at relativelyhigh temperatures. As a result, low yields have to be taken into accountif polymers are desired which have a relatively high molecular weight aswell as a relatively low degree of branching. Such polymers are howeverof commercial importance because they are distinguished by comparativelyhigh yield points and low elongation (particularly homopolymers) and alow melt index (particularly copolymers with a relatively high contentof comonomers).

The present invention has for its object to provide a process of thetype defined above with which it is possible to prepare polymers havinga high molecular weight and a low degree of branching in higher yields.

We have found that this object is achieved by using as polymerizationinitiator a mixture of two special types of free radical generatingpolymerization initiators.

In accordance with this invention the process involves the production ofhomopolymers or copolymers of ethylene by homopolymerization of ethyleneor by copolymerization of a mixture of 100 molar proportions of ethylenewith up to 100 molar proportions of another ethylenically unsaturatedmonomer containing three to carbon atoms which is copolymerizable withethylene at a pressure of 800 to 7,000 atmospheres and temperatures offrom 150 to 260 C, preferably from 165 to 235 C under the action of afree radical generating polymerization initiator with or' without apolymerization regulator. The polymerization initiator to be usedaccording to the invention in an amount of from 2 to 1,000, preferablyfrom 3 to 200, ppm molar (based on the total amount of monomers used)consists of a mixture of a. a free radical generating polymerizationinitiator which has a halflife of from 10 to 30 hours at 50 C; and

b. a free radical generating initiator which has'a halflife at 50 C offrom 12 minutes to 10 hours, with the provisos that l. the halflife at50 C of the polymerization initiator (a) is at least twice as long asthat of polymerization initiator (b); and

ll. the amount of either of the polymerization initiators (a) and (b) isat least 10 percent molar and preferably at least 25 percentmolar basedon the total molecular amount of the mixture.

The following may be said concerning the two special types of freeradical generating polymerization initiators to be used according to theinvention:

a. examples of free radical generating polymerization initiators havinga halflife at 50 C (TIL/50 C) of 10 to 30 hours which are suitable arebis-2,4-dichlorobenzoyl peroxide (Hid/50 C 18 hours), tert-butylperpivalate (BL/50 C 20 hours) and2,2'-azobis-(2,4-dimethylvaleronitrile) (l-lL/50 C 28 hours). Instead ofindividual initiators, a mixture of two or more such polymerizationinitiators may be used;

b. examples of suitable free radical generating polymerizationinitiators having a halflife at 50 C (BL/50 C) of from 12 minutes to 10hours are acetylcyclohexanesulfonyl peroxide (l-lL/50 C 24 minutes),bis-(4-tert-butylcyclohexyl) peroxydicarbonate (HL/50 C 2 hours, 36minutes) and diisopropyl peroxydicarbonate (l-lL/50 C 6 hours). Insteadof an individual polymerization initiator, a mixture of two or more suchpolymerization initiators may be used.

It has been found that mixtures of:

(a) tert-butyl perpivalate and (b) bis-(4-tert-butylcyclohexyl)peroxydicarbonate; and of a. 2,2'-azobis-(2,4-dimethylvaleronitrile) andb. bis-(4-tert-butylcyclohexyl) peroxydicarbonate are extremely wellsuited.

Suitable equipment and procedures for carrying out the process accordingto the invention are those conventionally used for the polymerization ofethylene at superatmospheric pressure and elevated temperature. Insteadof giving further details, reference is made to Ullmanns Enzyklopadieder technischen Chemie, volume 14, third edition (Munich-Berlin 1963)chapter on polyethylene, pages 137 to 148, or to Lyle F. Albright,High-Pressure Processes for Polymerizing Ethylene, Chemical Engineering,volume 73 (1966) issue of December 19, pages 113 to 120.

Comonomers for ethylene in the copolymerization are those conventionallyused (within the above definition), particularly those which havemonoethylenic unsaturation. Examples of suitable comonomers are vinylesters, particularly of C to C alkanecarboxylic acids; esters of acrylicand methacrylic acid, particularly with C to C alkanols; esters ofmonoethylenically unsaturated dicarboxylic acids, particularlymonoesters and diesters of maleic and fumaric acids with C to Calkanols; monoethylenically unsaturated carboxylic acids, particularlyacrylic, methacrylic, maleic and fumaric acids; amides ofmonoethylenically unsaturated carboxylic acids, particularly acrylamide,methacrylamide and N-monoalkylamides and N,N-dialkylamides (with C to Calkyl groups) of acrylic and methacrylic acids; vinyl ethers,particularly vinyl ethers of C to C alkanols, of phenol or a naphthol;monoethylenically unsaturated alcohols, particularly C to C alkenols;monoethylenically unsaturated aldehydes, particularly C to C alkenals;monoethylenically unsaturated ketones, particularly C to C, alkenones.The comonomers may be used as individuals or as mixtures of differentindividuals in the copolymerization. For the sake of completeness it mayalso be stated that a number of the said comonomers act (in knownmanner) as polymerization regulators.

It the process according to the invention, as already stated,polymerization regulators may be present. The amount of regulator, as iswell known, may vary so greatly according to the strength of theregulator and the other process conditions that it is impossible to givegenerally applicable statements regarding absolute values. In thecontext of regulators, reference may be made to G.A. Mortimer, J. Polym.Sci., Part A-l, 4 (1966), No. 4, pages 881 to 900.

As polymerization apparatus a tubular reactor is used such as isconventionally used in continuous highpressure polymerization ofethylene. The ratio of the diameter to the length of the tube is1:14,000. The tube is surrounded by a jacket tube for reception of aheat transfer medium. The jacket tube itself is subdivided into twozones operable independently of one another,

the first extending along two-fifths of the length of the tube (zone I)and the second along the remaining three-fifths (zone 11). At the end ofthe reaction tube there is a valve which serves (a) to control thepressure in the polymerization chamber and (b) to discharge the reactionproduct. Following this valve there are a conventional high pressureseparator and a conventional low pressure separator-for separating thepolymer obtained from unpolymerized substances, i.e'., mainly from theportion of the monomers which have not been involved in thepolymerization.

EXAMPLE 1 The reactor is fed at the inlet end with a mixture, compressedto 1,800 atmospheres, consisting of 1,000,000 parts by weight per hourof ethylene, 55 ppm molar per hour (based on the ethylene) of a mixtureof 35 ppm molar per hour of tert-butyl perpivalate and 20 ppm molar perhour of bis-(4-tert-butylcyclohexyl) peroxy-dicarbonate in one-twentiethmolar acetone solution and also 2,400 parts by weight per hour or methylketone (regulator). The heat transfer medium in zone (I) of the jacketis kept at a constant temperature of 165 C, and in zone (11) at 180 C;the reaction material thus reaches a temperature of 230 C by the heat ofreaction liberated.

150,000 parts by weight per hour of polyethylene is obtained per hour inthis way. Its physical data are: melt index (according to ASTM D 1238)4.0 g/l minutes; density (according to DIN 53,479/7.2) 0.9352 g/ccm;elongation at break 150 percent; resistance to tearing 107 kg/cm.

Comparative Experiment A The procedure described in Example 1 isfollowed exactly with the exception that 55 ppm molar per hour oftert-butyl perpivalate alone is used instead of the initiator mixture.In thisway only 85,000 parts by weight per hour of polymer-is obtained.

Comparative Experiment B The procedure described in Example 1 isfollowed exactly with the only exception that 55 ppm per hour ofbis-(4-tert-butylcyclohexyl) peroxy-di'carbonate alone is used insteadof the initiator mixture. In this way only 120,000 parts by weight perhour of polymer is obtained.

EXAMPLE 2 The reactor is fed at the inlet end with a mixture, compressedto 2,300 atmospheres, consisting of 970,000 parts by weight per hour ofethylene, 30,000 parts by weight per hour of methyl methacrylate, 38 ppmmolar per hour (with reference to the whole amount of monomers used) ofa one-twentieth molar acetone solution of a mixture of 15.7 ppm molarper hour of 2,2-azobis-(2,4-dimethylva1eronitrile) and 22.3 ppm molarper hour of bis-(4-tert-butylcyclohexyl) perpxydocarbonate and 3,400parts by weight per hour of methyl ethyl ketone (regulator). The heattransfer medium is kept at a constant temperature of C in zone (I) ofthe jacket and at C in zone (II). The reaction material reaches atemperature of 220 C by the heat of reaction.

In this way 165,000 parts by weight per hour of a copolymer is obtained.Its physical data are: units of methyl methacrylate in the polymer:14.0percent'by weight (based on the weight of polymer); melt index (ASTMD 1238) 4.1 g/l0 minutes; density (DIN 53,479/7.2) 0.9331 g/ccm;elongation at break 630; tear resistance 156 kg/cm ComparativeExperiment A The exact procedure of Example 2 is followed with the onlyexception that 38 ppm molar per hour of 2,2-azobis-(2,4-dimethylvaleronitrile) alone is used instead of theinitiator mixture. Only 130,000 parts by weight per hour of polymer isobtained in this way.

Comparative Experiment B The exact procedure of Example 2 is followedwith the only exception that 38 ppm molar per hour of bis-(4-tert-butylcyclohexyl) peroxydicarbonate alone is used instead of theinitiator mixture. Only 135,000 parts by weight per hour of polymer isobtained in this way.

EXAMPLE 3 The reactor is fed at the inlet end with a mixture, compressedto 2,100 atmospheres, consisting of 730,000 parts by weight per hour ofethylene, 270,000 parts by weight per hour of vinyl acetate and 6.1 ppmmolar per hour (with reference to the whole amount of monomers used) ofa one-twentieth, molar acetone solution of a mixture of 4.1 ppm molarper' hour of tertbutyl perpivalate and 2.0 ppm molar per hour of bis-(4-tert-butylcyclohexyl) peroxydicarbonate. The heat transfer medium iskept at a constant temperature of 165 C in zone (I) of the jacket and at180 C in zone (11). The reaction material reaches a maximum temperatureof C by the heat of reaction. I

170,000 parts by weight per hour of a copolymer is obtained in this way.Its physical data are: units of vinyl acetate in the polymer: 24.8percent by weight (based on the weight of polymer); melt index (ASTM D1238) 3.7 g/l0 minutes; density (DIN 53,479/7.2) =0.9503 g/ccm;elongation at break 730 percent tear resistance 248 kg/cm.

Comparative Experiment A The exact procedure of Example 3 is followedwith the sole exception that 6.1 ppm molar per hour of tertbutylperpivalate alone is used instead of the initiator mixture. Only 137,000parts by weight per hour of polymer is obtained in this way.

Comparative Experiment B The procedure of Example 3 is followed exactlywith the one exception that 6.1 ppm molar per hour of bis-(4-tert-butylcyclohexyl) peroxydicarbonate is used instead of theinitiator mixture. Only 145,000 parts by weight of polymer is obtainedin this way per hour.

We claim:

1. A process for the production of a homopolymer or copolymer ofethylene by homopolymerization of ethylene or by copolymerization of amixture of 100 molar proportions of ethylene and up to 100 molarproportions of at least one other ethylenically unsaturated monomerwhich has from three to twenty carbon atoms and which is copolymerizablewith ethylene at a pressure of from 800 to 7,000 atmospheres and atemperature of from 150 to 260 C under the influence of a free radicalgenerating polymerization initiator and with or without a polymerizationregulator, wherein there is used as the polymerization initiator in anamount of from 2 to 1,000 ppm molar (with reference to the whole amountof monomers used) a mixture of a. a free radical generatingpolymerization initiator which has a halflife of from to 30 hours at 50C and b. a free radical generating polymerization initiator which has ahalflife of from 12 minutes to 10 hours at 50 C, with the provisos thatI. the halflife of the polymerization initiator (a) at 50 C is at leasttwice that of the polymerization initiator (b).and

II. the amount of (a) or (b) in the mixture of polymerization initiatorsis not less than 10 percent molar in either case (with reference to thetotal molecular amount of the mixture).

2. A process as claimed in claim 1 carried out at from to 235 C.

3. A process as claimed in claim 1 wherein the amount of initiator usedis from 3 to 200 ppm 'mol ar based on the total amount of monomers used.

4. A process as claimed in claim 1 wherein the amount of each of thepolymerization initiators in the mixture of (a) and (b) is at least 25percent molar based on the total molecular amount of the mixture.

5. A process as claimed in claim 1 wherein initiator (a) isbis-2,4-dichlorobenzoyl peroxide, tert-butyl perpivalate or2,2-azobis-(2,4-dimethylvaleronitrile).

6. A process as claimed in claim 1 wherein initiator (b) isacetylcyclohexanesulfonyl peroxide, bis-(4-tertbutylcyclohexyl)peroxydicarbonate or diisopropyl aeroxydicarbonate.

7. A process as claimed in claim 1 wherein initiator (a) is tert-butylperpivalate or 2,2'-azobis-(2,4 dimethylvaleronitrile) and initiator (b)is bis-(4-tertbutylcyclohexyl) peroxydicarbonate.

1. A process for the production of a homopolymer or copolymer ofethylene by homopolymerization of ethylene or by copolymerization of amixture of 100 molar proportions of ethylene and up to 100 molarproportions of at least one other ethylenically unsaturated monomerwhich has from three to twenty carbon atoms and which is copolymerizablewith ethylene at a pressure of from 800 to 7,000 atmospheres and atemperature of from 150* to 260* C under the influence of a free radicalgenerating polymerization initiator and with or without a polymerizationregulator, wherein there is used as the polymerization initiator in anamount of from 2 to 1, 000 ppm molar (with reference to the whole amountof monomers used) a mixture of a. a free radical generatingpolymerization initiator which has a halflife of from 10 to 30 hours at50* C and b. a free radical generating polymerization initiator whichhas a halflife of from 12 minutes to 10 hours at 50* C, with theprovisos that I. the halflife of the polymerization initiator (a) at 50*C is at least twice that of the polymerization initiator (b) and II. theamount of (a) or (b) in the mixture of polymerization initiators is notless than 10 percent molar in either case (with reference to the totalmolecular amount of the mixture).
 2. A process as claimed in claim 1carried out at from 165* to 235* C.
 3. A process as claimed in claim 1wherein the amount of initiator used is from 3 to 200 ppm molar based onthe total amount of monomers used.
 4. A process as claimed in claim 1wherein the amount of each of the polymerization initiators in themixture of (a) and (b) is at least 25 percent molar based on the totalmolecular amount of the mixture.
 5. A process as claimed in claim 1wherein initiator (a) is bis-2,4-dichlorobenzoyl peroxide, tert-butylperpivalate or 2,2''-azobis-(2,4-dimethylvaleronitrile).
 6. A process asclaimed in claim 1 wherein initiator (b) is acetylcyclohexanesulfonylperoxide, bis-(4-tert-butylcyclohexyl) peroxydicarbonate or diisopropylaeroxydicarbonate.